1. Field of the Invention
One embodiment of the present invention relates to an imaging device including an oxide semiconductor.
Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. In addition, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specifically, examples of the technical field of one embodiment of the present invention disclosed in this specification include a semiconductor device, a display device, a liquid crystal display device, a light-emitting device, a lighting device, a power storage device, a memory device, an imaging device, a method for driving any of them, and a method for manufacturing any of them.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A transistor and a semiconductor circuit are embodiments of semiconductor devices. In some cases, a memory device, a display device, an imaging device, or an electronic device includes a semiconductor device.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) and a display device. Although silicon-based semiconductors have been widely used as semiconductor materials which can be used for the transistors, oxide semiconductors have been attracting attention as alternative materials.
For example, a technique for forming a transistor using zinc oxide or an In—Ga—Zn-based oxide semiconductor as an oxide semiconductor is disclosed (see Patent Documents 1 and 2).
Patent Document 3 discloses an imaging device where a transistor including an oxide semiconductor with an extremely low off-state current is used in part of a pixel circuit and a transistor including silicon with which a complementary metal oxide semiconductor (CMOS) circuit can be formed is used in a peripheral circuit.
Patent Document 4 discloses an imaging device in which a transistor including silicon, a transistor including an oxide semiconductor, and a photodiode including a crystalline silicon layer are stacked.